EP0319354B1 - Driving device of a toothed wheel by way of a self-aligning pinion - Google Patents

Abstract

Device for driving a ring gear (2) by way of a floating drive pinion (1) mounted inside a carriage (3) comprising rollers (4) which roll on internal tracks (2a) concentric with the teeth of the ring gear and hold the carriage (3) radially on the said ring gear at the operating spacing by a resilient member, characterised in that the drive pinion (1) and the ring gear (2) have teeth of the "set back" type, such that the maximum diameter of the profiles in contact with the ring gear is smaller than the reference operating diameter of the said ring gear, which produces, in operation, a single direction of sliding on the teeth. <IMAGE>

Description

The subject of the present invention is a device for driving a toothed ring by a self-aligning floating pinion, intended in particular for driving at low speed a large toothed ring.

It is known that to transmit, by a pinion mounted in fixed bearings, a rotational movement to a crown with external toothing of large diameter on which the precision of production is difficult to obtain because of the large dimensions, it is practically impossible to obtain a good bearing capacity of the teeth flanks over the entire cut width.

Indeed, the ring gear is fixed on a shaft or on a tube whose centering precision, as of rotation is variable because of the deformations due to the flexibility of the material and to the variations of the transmitted forces as well as to the dilations by change of temperature, which causes rapid deterioration of these materials.

For these reasons, there is known in FR-A-1 230 485, a device for driving a ring gear in which the floating motor pinion is mounted inside a carriage comprising rollers which roll on tracks concentric with the teeth of the ring gear and thus radially maintain the carriage on said ring gear at the operating center distance. This carriage is held fixed by a drawbar located in the median plane of the teeth and fixed, on the one hand, to a joint on the carriage and connected, on the other hand, to a fixed part, by a ball joint .

Also known, in FR-A-1 464 558, is a device in which the floating pinion is mounted in a support which is supported by three bars hinged at their ends. Two of these bars are substantially parallel to the plane formed by the axes of the pinions and of the crown and are located on either side of the crown and of the aforementioned plane and the outer tracks of the crown are located on either side. of the teeth or in the center of the cutting.

Generally, in the devices used until now, the ring gear and the drive pinion mesh together using straight teeth.

However, in the straight teeth used for this kind of material, the friction of the teeth changes direction when the contact point progressively moves from the tooth base to the top of the tooth passing through the primitive operating circle where the friction cancels out. and reverses. The change in sliding direction produces an angular offset of the contact force on either side of the line of action, which produces a very high variation in radial loads with each passage from tooth to tooth.

This variation in radial loads supported by the rollers causes an undulation of the tracks of the crown on which the rollers of the carriage supporting the motor pinion roll, which generates vibrations on said carriage and therefore gives very poor conditions of use, so much so that after a certain operating time, it is necessary to correct the tracks of the crown.

To avoid the undulation of the tracks of the crown, many manufacturers have increased the width of the tracks to reduce the pressure on the rollers, but this modification being applied to large crowns, considerably increases their weight, their machining and overall their production cost.

The present invention therefore aims to avoid these drawbacks and relates to a device for driving a ring gear by a floating motor pinion mounted inside a carriage comprising rollers which roll on concentric inner tracks to the toothing of the toothed ring and radially maintain the carriage on said toothed ring at the operating center distance by an elastic member, characterized in that the drive pinion and the toothed ring have a toothing offset so that the maximum diameter contact profiles of the ring gear is smaller than the original diameter of operation of said ring gear which produces in operation a single direction of sliding on the teeth.

According to another characteristic of the invention, the elastic member for keeping the rollers in contact on the inner tracks of the ring gear is constituted by an elastic traction crutch acting on the carriage.

• _ la Fig. 1 est une vue schématique d'une couronne dentée et d'un pignon moteur engrénant ensemble à l'aide d'une denture droite selon les réalisations antérieures de ce type de matériel,
• _ la Fig. 2 est une vue schématique d'une couronne dentée et d'un pignon moteur selon l'invention,
• _ la Fig. 3 est une vue en plan du dispositif d'entraînement selon l'invention,
• _ la Fig. 4 est une vue en coupe selon la ligne 4-4 de la Fig. 3,
• _ la Fig. 5 est un diagramme qui représente la variation de l'effort de contact dynamique en fonction de l'angle d'inclinaison de la barre d'attelage.

The invention will be better understood with the aid of the description which follows, given solely by way of example and made with reference to the appended drawings, in which:

• _ Fig. 1 is a schematic view of a ring gear and of a driving pinion meshing together using straight teeth according to the prior embodiments of this type of material,
• _ Fig. 2 is a schematic view of a ring gear and a driving pinion according to the invention,
• _ Fig. 3 is a plan view of the drive device according to the invention,
• _ Fig. 4 is a sectional view along line 4-4 of FIG. 3,
• _ Fig. 5 is a diagram which represents the variation of the dynamic contact force as a function of the angle of inclination of the drawbar.

Referring first to FIG. 1, we will examine the contact force between the floating drive pinion 1 and the large ring gear 2 transmitted by a tooth and the reaction it causes on the radial rollers supporting said drive pinion.

In general, the floating motor pinion 1 is mounted inside a carriage 3 (Fig. 3) comprising rollers 4 which roll on tracks 2 a concentric with the teeth of the ring gear and thus maintain radially the carriage 3 on said ring gear at the operating center distance using an elastic member.

01

= axe de pignon

02

= axe de couronne

I

= point de contact des dentures sur les cercles primitifs de fonctionnement

A

= point de contact sur un rayon plus grand que Rp

B

= point de contact sur un rayon plus petit que Rp

Rp

= rayon primitif de fonctionnement de la couronne dentée

Re

= rayon de tête de dent de couronne dentée (rayon maximum des profils de contact)

rp

= rayon primitif de fonctionnement du pignon

Rb

= rayon de base de la couronne

α

= angle de pression de denture (α = 20°)

φ

= angle de frottement des dentures

tg φ

= coefficient de frottement des dentures

T1T2

= ligne d'action de l'engrenage

C

= couple résistant appliqué sur la couronne

S

= sens de rotation de la couronne

Fn

= effort de contact statique des dentures

F

= effort de contact dynamique des dentures (décalé de l'angle de frottement).

In Fig. 1, according to the prior art, the driving pinion 1 and the crown 2 mesh together using a straight toothing whose geometric characteristics of the toothing and the values of the forces transmitted are designated by:

01

= pinion axis

02

= crown axis

I

= point of contact of the teeth on the primitive operating circles

AT

= contact point on a radius larger than Rp

B

= point of contact on a radius smaller than Rp

Rp

= original operating radius of the ring gear

Re

= radius of toothed crown tooth head (maximum radius of contact profiles)

rp

= original operating radius of the pinion

Rb

= base radius of the crown

α

= toothing pressure angle (α = 20 °)

φ

= tooth friction angle

tg φ

= coefficient of friction of the teeth

T1T2

= gear line of action

VS

= resistant torque applied to the crown

S

= direction of rotation of the crown

Fn

= static contact force of the teeth

F

= dynamic contact force of the teeth (offset from the friction angle).

In the straight teeth used until now in this kind of material, the friction of the teeth changes direction when the contact point progressively moves from the tooth base to the top of the tooth passing through the primitive circle (point I) where the friction cancels and reverses. The change in sliding direction produces an angular offset of the contact force on either side of the line of action T1, T2 (friction cone).

dans la zone de contact IA.

dans la zone de contact IB.For a constant resistant torque C on the crown 2 to be transmitted by the pinion 1 on said crown by the dynamic contact force F, depending on the position of the contact described above, the force F will have as value:

in the IA contact area.

in the IB contact area.

pour les deux zones IA et IB.The second term of the denominators (IA sin φ and IB sin φ) contributes to increasing the difference between the two values of F in the zones IA and IB. But, since these terms can take values close to zero, when the contact points approach point I, we will not take them into account as a first approximation and we will take the simplified value:

for the two zones IA and IB.

To know the forces due to the meshing, applied to the radial holding elements of the pinion 1 on the crown 2, it is necessary and sufficient to take the projection of this value on the axis OX, that is:

This value Fx contains two constant terms, C and Rp and a variable term tg (α ± φ) where the angle of friction φ changes direction.

The ratio of the two values of Fx in the contact zones IA and IB is written:

The values of the coefficient of friction (tgφ) according to various parameters such as load, speed, lubrication, etc ... and for gears operating at low speed, are around 0.07 to 0.08, but can reach 0.15 for very low speeds.

ce qui représente la variation de charge sur les galets 4.By taking, for example, the minimum value of tgφ, that is 0.07 and α = 20 ° corresponding to a standardized toothing, we see that the ratio of the two values of Fx in the zones IA and IB takes the value:

which represents the load variation on the rollers 4.

This charge variation is very high and can clearly exceed the value 1.55 for values of tg φ greater than 0.07. This variation in load occurring at each passage from tooth to tooth, causes an undulation of the tracks 2 a of the crown 2, which generates vibrations on the carriage 3 comprising the drive pinion 1 and therefore gives very poor operating conditions.

To avoid the formation of undulations on the tracks of the crown, the driving pinion 1 and the toothed crown 2 according to the present invention have a toothing offset, which allows operation with a single direction of sliding and, therefore , the elimination of tooth-to-tooth load variations on the pinion holding rollers on the crown.

In Fig. 2, where the designation of the elements is identical to FIG. 1, the pinion 1 and the crown 2 have a toothing of the "retreating" type, so that the maximum contact diameter of the crown is smaller than the original operating diameter of said crown.

quelle que soit la position de contact des dentures.Indeed, the two points A and B of contact of the teeth are located on the same side of the contact point I on the line T1T2, therefore on a radius smaller than the original radius Rp of operation of the ring gear, which causes a single direction of sliding, hence the absence of variation of forces on the radial holding elements of the pinion 1, since Fx is then written:

whatever the contact position of the teeth.

As shown in Figs. 3 and 4, the pinion 1 is integral with a motor shaft 5 which rotates in the carriage 3 by means of bearings 6.

The carriage 3 comprises at its upper part four symmetrical rollers 4 in pairs, which roll on the tracks 2a formed on the internal face of the crown 2 and concentric with the teeth of said crown.

The carriage 3 is held by a drawbar 7 located in the median plane of the teeth and fixed, on the one hand, to a hinge 8 on said carriage and, on the other hand, connected to a fixed part on a ball joint 9 .

In addition, maintaining contact with rollers 4 on the inner tracks 2 a , which fixes the operating distance, is produced by an elastic traction stand 10 located in the median plane of the crown teeth and on the line of the centers of the pinion 1 and the crown 2 The elastic traction stand 10 acts on the carriage 3 so that the running-in or wear of the tracks and rollers only causes an increase in the operating center distance, which makes it possible to maintain operation with a single direction of sliding. , since in the case of wear, the difference between the maximum diameter of the contact profiles of the ring gear and the original operating diameter increases. On the other hand, if any wear causes a reduction in the operating distance, the above-mentioned difference decreases and can be reversed (maximum diameter of the contact profiles larger than the original operating diameter), which in in this case, brings the operation to two sliding directions. This remark is important since the theoretical difference between the original operating diameter and the maximum diameter of the crown contact profiles is small.

The lower part of the carriage 3 is provided with a yoke 11 connected to one end of the stand 10 by an axis 12. The stand 10 is constituted by a cylinder 10 a articulated on the axis 12 and comprising an internal chamber 10 b to inside which slides a piston 10 c . This piston 10 c is extended by a rod 10 d which opens outside the internal chamber 10 b and the end of which is articulated by a pin 13 on a yoke 14 connected to a fixed part.

Belleville washers are interposed between the piston 10 c and the bottom of the internal chamber 10 b so as to exert traction on the carriage 3 and keep the rollers 4 in contact on the inner tracks 2 a of the ring gear 2.

This pull stand is necessary when the position of the carriage 3 on the ring gear 2 is such that a component of its own weight can cancel the effort of separation of the teeth, thus modifying the operating distance which is not in this case limited only by the contact of the two conjugate profiles of the teeth. This phenomenon can occur for each variation in torque, that is to say, for example, when starting or braking or when accelerating or decelerating, and cause major disturbances.

The description of the invention which has just been given relates to a particular case where the drawbar 7 is parallel to the axis Oy (Figs 1 and 2). On different types of apparatus with particular functioning, such as for example a winch where there is only one direction of torque to be transmitted on the crown, the drawbar 7 can be tilted by an angle β (figure 3) to reduce the loads on the rollers 4. But, in this case, with normal toothing with two sliding directions, the ratio of the values Fx in the contact zones IA and IB increases considerably.

This appears on the diagram in Fig. 5 which represents the variation of Fx as a function of the angle β and where the axis of the abscissas represents the variations of the angle β and the axis of the ordinates the variation of the values of Fx.

où il a été donné à $$\frac{\text{C}}{\text{Rp}}$$

une valeur constante de 10 et avec (tg α _ φ) = 16° pour la courbe A et (tg α + φ) = 24° pour la courbe B.Curves A and B represent the variations of Fx as a function of the angle β according to the formula

where it was given to $$\frac{\text{VS}}{\text{Rp}}$$

a constant value of 10 and with (tg α _ φ) = 16 ° for curve A and (tg α + φ) = 24 ° for curve B.

Curves C represent the variation of the loads Fx represented by the ratio of the values of curve A and B.

Examination of these curves reveals the significant excitation (curves C) produced by the change of direction of sliding on the teeth with two directions of sliding and shows the advantage of using teeth with one direction of sliding for this type of material which is floating, therefore very sensitive to vibrational excitations, which represents an essential characteristic of the present invention.

The use of a driving pinion and a toothed ring having a toothing offset which allows operation with a single direction of sliding on the teeth, therefore avoids the formation of undulations on the tracks of the toothed ring, which very significantly improves the conditions of use of the device.

Claims (5)

1. Device for driving a crown gear (2) by a floating motor pinion (1) mounted within a carriage (3) having rollers (4), which roll on internal tracks (2a) concentric to the tooth system of the crown gear (2) and which radially maintain the carriage (3) on said crown gear with the operating distance between centres by an elastic member (10), characterized in that the motor pinion (1) and the crown gear (2) have a tooth system offset, in such a way that the maximum diameter of the contact profiles of the crown gear is smaller than the operating pitch diameter of said crown gear, so that, in operation, there is a single sliding direction on the tooth systems.

2. Drive device according to claim 1, characterized in that the elastic member for keeping the rollers (4) in contact with the internal tracks (2a) of the gear (2) is constituted by an elastic, tension T-handle (10) acting on the carriage (3).

3. Drive device according to claim 2, characterized in that the elastic tension T-handle (10) is located in the median plane of the tooth system of the gear (2) and on the centre line of the pinion (1) and the gear (2).

4. Drive device according to claims 1 and 2, characterized in that the elastic, tension T-handle (10) is constituted by a cylinder (10a) articulated to the carriage (3) and having an internal chamber (10b) within which slides a piston (10c) extended by a rod (10d), whose end is articulated to a yoke (14) connected to a fixed part.

5. Drive device according to claim 4, characterized in that the internal chamber (10b) has cupped washers (15) interposed between the piston (10c) and the bottom of the said chamber.

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